Polyacetal polymers, which are commonly referred to as polyoxymethylenes (POMs), have become established as exceptionally useful engineering materials in a variety of applications. POMs for instance, are widely used in constructing molded parts, such as parts for use in the automotive industry and the electrical industry. POMs, for instance, have excellent mechanical property, fatigue resistance, abrasion resistance, chemical resistance, and moldability.
Polyacetal resins also have a tendency to be relatively stiff and rigid. Thus, the polymers have impact strength characteristics that make them not well suited to some applications. In order to improve impact strength, polyacetal resins have been combined in the past with impact modifiers. Typical impact modifiers that have been employed have included aromatic polyurethanes and polymethacrylate butadiene styrene (MBS) acrylic-type modifiers. Adding the above impact modifiers to a polyacetal resin can significantly improve the impact strength of molded articles made from the combination of components. Unfortunately, however, the above impact modifiers have a tendency to discolor when exposed to ultraviolet light and/or heat. Attempts to stabilize the above compositions using commercially available UV stabilizers have been met with limited success. Thus, the above impact modified polyacetal resins have not been well suited for use in some applications.
For example, interior automotive parts are now required to have increased ductile properties for reasons related to passenger safety and for increasing aesthetic appeal. Such parts can include, for instance, trim pieces, visor clips, trim bezels, handles, airbag covers, and the like. Automotive manufacturers now desire that the above parts be flexible and ductile as opposed to being brittle and stiff. In order to meet the above requirements, polyacetal resins can be combined with the above described impact modifiers. Adding impact modifiers in order to increase the ductile properties of the parts, however, adversely affects the ability of the part to resist fading when subjected to ultraviolet light and the typical thermal cycles that interior automotive parts are subjected to during use.
In view of the above, a need currently exists for a composition containing a polyacetal resin that is not only ductile but is substantially stable when exposed to ultraviolet light and/or thermal cycles.